The present invention relates to an internal electrode type plasma processing apparatus and plasma processing method, more particularly, relates to a plasma processing apparatus and plasma processing method provided with an inductive coupling type electrode suited for deposition of an amorphous silicon thin film used for solar cells or thin film transistors and the like on a large-area substrate.
The electrodes of internal electrode type plasma CVD apparatuses have conventionally been of the parallel-plate type or the inductive coupling type.
If using the parallel-plate type electrode, when trying to raise frequency of a high frequency power in order to increase a film deposition rate and improve film characteristics, the problem arises that the electric discharge becomes non-uniform. This is caused by the occurrence of a standing wave on the electrode plate resulting on non-uniform distribution of plasma density and by the production of plasma at undesirable locations due to the voltage created by the feedback current to the ground. Further, as the substrate holder is made to function as a ground electrode, the backing plate for the substrate becomes required and there is the difficulty of maintaining the clearance between the backing plate and substrate uniform when the size of the electrode plate is increased so as to form a film on a large-area substrate. Also, handling of the backing plate becomes difficult generally. Therefore, a parallel-plate type electrode is not well suited to the deposition of a film on a large-area substrate.
As opposed to the above parallel-plate type electrode, an inductive coupling type electrode is free from the above problems. Accordingly, the inductive coupling type electrode is well suited to the deposition of a film on a large-area substrate when used in an internal electrode type plasma CVD apparatus, for example.
As an internal electrode type plasma CVD apparatus using an inductive coupling type electrode, for depositing an amorphous silicon thin film on a large-area substrate to form a solar cell etc, there is the apparatus disclosed in Japanese Unexamined Patent Publication (Kokai) No. 4-236781, for example. In this plasma CVD apparatus, the electrode for discharge is formed by a flat coil having a ladder-like structure which is arranged parallel to the substrate. The ladder-like flat coil is formed by a conductive wire. The source gas is introduced from a reaction gas introduction pipe provided at a single location of the reactor, while the inside of the reactor is evacuated through an evacuation pipe provided at a single location of the reactor. This flat coil increases the intensity of the electromagnetic field and improves the uniformity of the field. Further, as a similar conventional plasma CVD apparatus, there may be the apparatus disclosed in Japanese Patent No. 2785442. In this plasma CVD apparatus, as the electrode arranged facing the substrate, a flat coil electrode formed by a single conductive wire bent multiple times to form a zigzag configuration is used. A high frequency power is supplied from a high frequency generator to the two ends of this electrode.
Concerning the above inductive coupling type electrode, the ladder-shaped flat coil electrode according to Japanese Unexamined Patent Publication (Kokai) No. 4-236781 does not have a uniform current flowing at each rung of the ladder configuration and therefore does not give a uniform distribution of the electromagnetic field, so has the problem of the inability to deposit a uniform film on the large-area substrate.
The ladder-shaped flat coil electrode is a distributed constant circuit in view of an electric circuit. A current flowing at each section in the distributed constant circuit can not be calculated simply from resistance and path length of the circuit. In the ladder type electrode, an impedance of each ladder rung relative to other ladder rungs and a geometrical relation between each ladder rung and a feeding point is related to the magnitude of Poynting vector at each ladder rung. Experimentally, the phenomenon that most of the current flows at the ladder rung near the feeding point is observed.
Further, since the zigzag flat coil electrode according to Japanese Patent No. 2785442 is produced by bending a single long conductive wire and the high frequency power is supplied from one end, the power cannot be fed efficiently. Further, while effort is made in the design to prevent the generation of a standing wave as much as possible, it is impossible to prevent the generation of a standing wave at undesirable locations due to the configuration of the electrode. Therefore, the film deposition is disturbed. That is, an unintentional standing wave is produced at the electrode, and this standing wave disturbs the distribution of plasma and results in poor uniformity of film deposition.
Then, in the plasma CVD apparatus and the like of the internal electrode type and inductive coupling type, it is desired to generate the plasma around the electrode by positively producing and utilizing the standing wave along the electrode arranged in the processing chamber. The plasma generated around the electrode receives energy for plasma generation from the antinode portion of the standing wave. Accordingly, it is preferred to control the standing wave generated along the electrode and the number or the positions of the antinodes to be formed in a desirable situation. Thereby, the standing wave can be actively used in a controllable state so that the antinodes are produced at desirable positions along the electrode, and therefore it is possible to skillfully control a distribution of plasma and to deposit a film on a large-area substrate with a good situation.
Further, as a general discussion, when proposing an electrode configuration in the internal electrode type plasma processing apparatus, concerning the standing wave positively produced on the electrode, the relationship between the frequency of the high frequency power supplied to the electrode and plasma produced around the electrode in the reactor due to the high frequency power sometimes cannot be ignored. Further, the plasma exited around the electrode due to the standing wave formed on the electrode, specifically the plasma parameters, have a major effect on the standing wave and sometimes make it necessary to reevaluate the design parameters of the electrode configuration. In this case, it is required that sufficient consideration be given to the plasma parameters when designing the electrode.
The objective of the present invention is to solve the above problems, positively utilize a standing wave in a controllable state to achieve a good uniformity of the plasma density, realize a configuration of the electrode considering the plasma parameters around the electrode, and to provide an internal electrode type plasma processing apparatus and plasma processing method which is suitable for deposition of a film on a large-area substrate for a solar cell etc.
The internal electrode type plasma processing apparatus and method according to the present invention are configured so as to achieve the above objects.
The plasma processing apparatus of the present invention is the apparatus of the internal electrode type provided with an inductive coupling type electrode arranged in a vacuum processing chamber. The above electrode is formed so that the total length thereof is substantially equal to an excitation wavelength, and one end of the electrode is grounded and another end is connected to a high frequency power source. A standing wave of one wavelength is produced along the electrode when the high frequency power source supplies a high frequency power to the electrode. When producing the standing wave on the electrode, a node of the standing wave along the electrode is formed at a central portion of the electrode, and antinodes of the standing wave are formed at half portions of said electrode, which exists at both sides of a center point.
Each part of the standing wave, which are produced on the halves of the electrode, are mutually intensified to supply the electromagnetic energy to the surrounding space of the electrode, and the plasma of uniform density is generated in the surrounding space of the electrode. When generating the plasma within the processing chamber, active use of the standing wave positively generated on the electrode is performed.
In the above plasma processing apparatus, the electrode is formed to be U-shaped by bending it back at the central portion, and each of the half portions of the electrode corresponds to a straight portion, and both half portions are arranged in parallel.
In the above plasma processing apparatus, the length of the half portion of the electrode is substantially equal to a half of the wavelength of the supplied high frequency power.
In the above plasma processing apparatus, a plurality of the electrodes are arranged to make a stratified structure comprising a plurality of layers within the vacuum processing chamber, a plurality of film depositing regions are produced using the space between the electrodes included in the plurality of layers, and film deposition on a substrate is performed in each of the plurality of film depositing regions. This structure can increase a processing efficiency of substrates.
The plasma processing apparatus of the present invention is the apparatus of an internal electrode type, which is provided with an inductive coupling type electrode in a vacuum processing chamber, and the electrode is formed so that a total length of the electrode is determined to natural number times of a half of an excitation wavelength, one end of the electrode is grounded and another end thereof is connected to a high frequency power source, and standing waves are produced along the electrode when the high frequency power source supplies a high frequency power to the electrode, and further a node of the standing waves produced along the electrode is formed at a central portion of the electrode, and at least one antinode of the standing waves is formed at half portions of the electrode, which exist at both sides of a center point.
In the above plasma processing apparatus, the electrode is formed to be U-shaped by bending it back at the central portion, and each of the half portions of the electrode is a straight portion, both of the half portions are arranged in parallel, and the node of the standing wave is consistent with a bending back point.
In the above plasma processing apparatus, a plurality of electrodes are arranged to make a stratified structure comprising a plurality of layers within the vacuum processing chamber, a plurality of film depositing regions are produced using the space between the electrodes included in the plurality of layers, and film deposition on a substrate is performed in each of the plurality of film depositing regions.
The plasma processing apparatus of the present invention comprises a plurality of electrodes of an inductive coupling type in a vacuum processing chamber, and each of the plurality of electrodes is formed by bending back a conductor at its central portion to be U-shaped, the straight portions formed by the bending back are made parallel and are arranged to be in one plane, and further one end of each of the electrodes is grounded and another end thereof is connected to a high frequency power source. Further, the plurality of electrodes positioned parallel to each other are placed so that a straight portion of a power supplying side is adjacent to a straight portion of a grounded side, and high frequency powers respectively supplied into the ends of the straight portions of power supplying side for the plurality of electrodes are in phase.
In the above plasma processing apparatus, the length of each straight portion formed by bending back the plurality of electrodes is determined to produce an antinode of a standing wave on the straight portion.
In the above plasma processing apparatus, plural electrodes arranged to be in one plane is configured as an electrode array, a plurality of the electrode arrays are placed as a stratified structure within the vacuum processing chamber, a plurality of film depositing regions are produced using a space between said electrode arrays of plural layers, and film deposition on a substrate is performed in each of the plurality of film depositing regions.
The plasma processing apparatus of the present invention comprises an electrode of an inductive coupling type in a vacuum processing chamber and the electrode is formed by bending back a conductor at its central portion to be U-shaped. Further, a plasma discharge is produced around the electrode by supplying a high frequency power to an end of the electrode so that a standing wave of half wavelength is produced at a straight portion formed by bending back the electrode. In this case, frequency (f) of the high frequency power at this time is determined by f=(c/{square root over ( )}∈p)/2L1, where c is the speed of light, L1 is the length of the straight portion formed by bending back the electrode, and ∈p is the relative dielectric constant of plasma produced around the electrode.
In the above plasma processing apparatus, the frequency of the high frequency power is changed according to plasma parameters around the electrode.
In the above plasma processing apparatus, a plasma CVD processing is performed for depositing a film with a solar cell function on a large area substrate within the vacuum processing chamber.
In the above plasma processing apparatus, the length L1 of the electrode is preferred to be more than 0.8 meter.
The plasma processing method of the present invention is the processing method executed in the plasma processing apparatus having an electrode of an inductive coupling type placed within a vacuum processing chamber, and the plasma processing method is characterized in that the electrode is formed by bending back a conductor at its central portion, a total length of the electrode is determined to be a natural number times of a half of an excitation wavelength, a high frequency power is supplied to end of the electrode, a node of a standing wave produced in the electrode is consistent with a bending back point, and the standing wave makes density distribution of plasma around the electrode to be uniform.
The plasma processing method of the present invention is the method executed in a plasma processing apparatus comprising an electrode of an inductive coupling type in a vacuum processing chamber, and the electrode is formed by bending back a conductor at its central portion to be U-shaped, and a plasma discharge is produced around the electrode by supplying a high frequency power to an end of the electrode so that a standing wave of half wavelength is produced at a straight portion formed by bending back the electrode.
In the above plasma processing method, frequency (f) of the high frequency power at this time is determined by f=(c/{square root over ( )}∈p)/2L1, where c is the speed of light, L1 is the length of the straight portion formed by bending back the electrode, and ∈p is the relative dielectric constant of plasma produced around the electrode.
In the above plasma processing method, the frequency of the high frequency power is changed according to plasma parameters around the electrode.